A liquid crystal display device has advantages of thinness, light weight, and low power consumption compared with CRT (cathode ray tube) and is applied as a display device of a personal computer, a mobile phone, a digital camera, or other electronic equipments.
The liquid crystal display device is roughly divided into a transmissive type and a reflective type. The liquid crystal display differs from CRT in that it is not self-luminescence type display. Therefore, a transmissive liquid crystal display is provided with a planar light source called a “backlight” as a light source at its back surface, in which a light illuminated from the backlight passes through a liquid crystal panel for display. Since the transmissive liquid crystal display device displays an image by using the backlight, it has advantages that it remains unaffected even when an intensity of an ambient light is weak and can display an image at a high luminance and a high contrast. However, the backlight consumes over 50% of the entire power consumption in the liquid crystal display, so the transmissive liquid crystal display device suffers from a disadvantage that a reduction of the power consumption is difficult. When the intensity of the ambient light is strong, the transmissive liquid crystal display device also suffers from disadvantages that the display thereof appears dark and the viewability deteriorates.
On the other hand, a reflective liquid crystal display device utilizes the ambient light as the light source, in which the ambient light is reflected by a reflection portion provided with for example a reflection plate, and the reflected light passes through a liquid crystal layer for display. The device displays an image on a screen by utilizing the ambient light, so the reflection plate thereof has a rough shaped surface for diffusing and reflecting a light. Such reflective liquid crystal display device differs from the transmissive liquid crystal display device in that it is not provided with the backlight, so it has an advantage of lower power consumption. However, when surroundings are dark, a reflection light is weak, consequently, disadvantages arise in that an insufficient luminance and contrast cause a deterioration of viewability. Particularly, in a color display, the reflected light is absorbed in a color filter, so an efficiency of utilization of the reflected light ends up falling, consequently, the viewability markedly deteriorates.
For overcoming the above disadvantages of the transmissive liquid crystal display device and the reflective liquid crystal display device, there is known a transflective liquid crystal display device in which the transmissive display and the reflective display are jointly used. The transflective liquid crystal display device displays an image by applying the reflection of the ambient light in a bright place or applying the backlight in a dark place.
FIG. 1 is a schematic view illustrating a configuration of a transflective liquid crystal display device in the related art. In FIG. 1, FIG. 1(A) is a plane view illustrating a surface portion of a first substrate 10, in which a color filter layer formed on a second substrate 80 is expressed by a dot line. FIG. 1(B) is a cross-sectional view illustrating a pixel portion of the liquid crystal display device along the line X1-X2 of FIG. 1(A).
As shown in FIG. 1, the transflective liquid crystal display device in the related art is provided with the first substrate 10, the second substrate 80, and a liquid crystal layer 19. The first substrate 10 is separately arranged to face the second substrate 80 and the liquid crystal layer 19 is arranged between the first substrate 10 and the second substrate 80.
A light transmission portion 11 and a light reflection portion 12 are formed in parallel in a pixel portion of the first substrate 10. The light reflection portion 12 of the first substrate 10 is a region for diffusing and reflecting the ambient light, and diffuses and reflects a front light illuminated from a second substrate 80 side through the liquid crystal layer 19. In the light reflection portion 12, a relief surface layer 50 is formed on the first substrate 10 so as to diffuse and reflect a light, and a reflection electrode 61 is formed to cover the relief surface layer 50. The reflection electrode 61 in the light reflection portion 12 is formed for example by silver.
The light transmission portion 11 is a region through which a light illuminated from the backlight passes. The backlight is provided at a surface side of the first substrate 10 opposed to the surface provided with the liquid crystal layer 19. In the light transmission portion 11, a transparent electrode (not shown) such as ITO (Indium Tin Oxide) is formed.
On the other hand, in the second substrate 80, a color filter layer 90 is formed for passing and coloring the front light and a back light. The color filter layer 90 includes a red color filter 90R, a green color filter 90B, and a blue color filter 90B of the primary colors as a set. Each of the color filters 90 is formed for example in a strip shape and overlapped each other so as to correspond to the entire region facing the light reflection portion 12 and the light transmission portion 11 of the first substrate 10.
When a display is performed by applying the transflective liquid crystal display device in the related art, in the light reflection portion 12, a front light L2 illuminated from a side to be a display surface of the second substrate 80 passes through the color filter layer 90, is reflected at the light reflection portion 12, passes through the color filter layer 90 and the liquid crystal layer 19, and illuminates the display surface of the second substrate 80, namely, the front light L2 passes through the color filter layer 90 twice. While, in the light transmission portion 11, a back light L1 illuminated from a first substrate 10 side passes through the liquid crystal layer 19 and the color filter layer 90, and illuminates the display surface of the second substrate 80, namely, the back light L1 passes through the color filter layer 90 just once. In the above way, the number of times passing through the color filter layer is different between the light reflection portion 12 and the light transmission portion 11. As a result, a luminance and a color purity are different between the light reflection portion 12 and the light transmission portion 11, so a color repeatability deteriorates.
In the transflective liquid crystal display device in the related art, the light reflection portion 12 and the light transmission portion 11 are formed in the entire surface in parallel, so a formation region of the light transmission portion 11 becomes narrow for example when a formation region of the light reflection portion 12 is enlarged in considering that the reflective display is important. Therefore, an improvement both of luminance and visibility each in the light reflection portion 12 and the light transmission portion 11 is difficult.
In the above way, in the related art, a display in a color image at a high color purity and a high luminance by applying a superior color representability is also difficult each in the light reflection portion 12 and the light transmission portion 11. Specifically, in the light reflection portion 12 in which the light passes through the color filter layer 90 twice, the luminance is drastically lowered and the visibility deteriorates, so an image quality of the display image is_sometimes insufficient.
Various method have been proposed for realizing an improvement of the image quality each in the light reflection portion 12 and the light transmission portion 11 when the transflective liquid crystal display device is applied and displayed (for example, referred to Patent Document 1)
Patent Document 1: Japanese Unexamined Patent Application (Kokai) No. 2000-111902